In an optical communication system, an optical interconnection, an optical disk device, etc., a light receiving device for converting an optical signal into an electric signal is used. FIG. 1 is a block diagram illustrating a configuration of a conventional example of a light receiving system. In FIG. 1, the system for gathering light output from an optical fiber 100 by a light-receiving element 102 such as a photodiode via a lens 101, for amplifying the output of the light-receiving element 102 by an amplification circuit 103, and for outputting the amplified output as an electric signal is used.
However, this system adopts the configuration for mounting the components by aligning an optical axis with the light-receiving element such as a photodiode in order to receive light from an optical fiber, an optical disk, etc. Therefore, the conventional system has a problem that the cost of parts including the lens, and the mounting cost are high. Especially, if a ribbon fiber where a plurality of optical fibers are arranged side by side is used, the cost of parts for aligning the optical axis of each optical fiber with a corresponding photodiode, and their mounting cost significantly increase.
Assume that the outer diameter (total diameter) of the optical fiber 100 is 100 μm, and the diameter of the core wire that actually transmits light is 10 μm in the light receiving system illustrated in FIG. 1. If the optical axis is misaligned, for example, by approximately several μms or less, conversion efficiency (OE conversion efficiency) from an optical signal into an electric signal is significantly decreased. Therefore, the alignment of the optical axis must be made with high precision in order to keep the OE conversion efficiency high, leading to an increase in the cost.
In the meantime, for example, increasing the diameter of the light-reception plane of the light-receiving element 102 such as a photodiode is considered to prevent the OE conversion efficiency from being decreased even if the optical axis is misaligned. However, a parasitic capacitance increases with an increase in the diameter of the light-receiving element, the response speed of the light-receiving element therefore drops, and a high-speed optical signal cannot be received. Accordingly, the demand for providing a light receiving device that reduces the cost required for aligning an optical axis and can receive a high-speed signal has been made.
Japanese Laid-open Patent Publication No. H1-138751, “Optical Sensor Array and Reading Device” as a conventional technique related to a connection between an optical fiber and a sensor discloses an optical sensor array and a reading device, which eliminate the need for a lens system and a self-focusing lens and improve the yield of a product by arranging an optical fiber unit within a light incident side translucent substrate of a photosensitive unit.
Additionally, Japanese Laid-open Patent Publication No. H6-350800, “Recognition Method for Substrate Having Optical Fiber Array and Semiconductor Device Using the Substrate” discloses a semiconductor device that can prevent quality degradation such as unevenness of a light quantity, etc. by recognizing an optical fiber array of an optical fiber array plate, and by mounting a semiconductor element at a predetermined position from the boundary face of the optical fiber array.
Furthermore, Published Japanese National Publication of International Patent Application No. H9-509494, “Method and Device for Detecting and Imaging Particles” discloses a method and a device for forming a digital image with high resolution in a format of a large spatial distribution of detected particles, for detecting the emission of particles from an emission source with an ultra-high sensitivity, and for quantifying the detected particles.
However, these conventional techniques cannot solve the problem that the cost for aligning an optical axis is high and the conversion efficiency from an optical signal into an electric signal significantly decreases when light output from, for example, an optical fiber is received with a photodiode if the optical axis is misaligned.